Sudden death

Wednesday I lost my best friend. She was a short haired grey tabby. She was only 10 years old. Never sick a day in her life. I got up as normal fed the dogs and as my dad woke up he found her dead at the foot of his bed on the floor. Her legs were streched out like she had been walking and fell over. I have four cats all very healthy and I have no idea what happened to her. To me there are only to possibities....a heart attack or getting something caught in her throat(she had a bad habit of eating any sort of paper product or strings) but I could find any signs of disturbance or obstruction in her throat. I keep wondering if I missed something. Or what else it could have been